Angled physical contact ferrule and associated method and apparatus for fabricating same

ABSTRACT

A ferrule is provided that can be fabricated in a repeatable and an efficient manner so as to have a relatively small apex offset. The ferrule includes a front face having a plateau defining a plane that extends perpendicular to the longitudinal axis and a hemispherical portion through which a longitudinal bore opens. The hemispherical portion is generally angled relative to the plateau and to the plane perpendicular to the longitudinal axis defined by the plateau. In this regard, a plane coincident with the centerline of the ferrule is disposed at an offset angle, typically between 8° and 12°, relative to the plane perpendicular to the longitudinal axis such that the resulting ferrule is an angled physical contact (APC) ferrule. A method and apparatus for fabricating the ferrule are also provided that grind a portion of the front face of the ferrule into a hemispherical shape with a relatively small apex offset regardless of the amount of material that is removed from the front face of the ferrule.

FIELD OF THE INVENTION

The present invention relates generally to ferrules for mounting uponthe end portions of optical fibers and, more particularly, to angledphysical contact (APC) ferrules and associated methods and apparatus forfabricating APC ferrules.

BACKGROUND OF THE INVENTION

A variety of ferrules have been developed to facilitate theinterconnection of optical fibers, with other optical fibers, opticaldevices or the like. For example, a number of standard ferrules, such asSC, FC, and ST ferrules, have been designed. Regardless of their type,ferrules typically define one or more longitudinal extending bores forreceiving end portions of respective optical fibers.

One common type of ferrule is an APC ferrule that is designed to makephysical conduct with another APC ferrule during the process ofinterconnecting a pair of optical fibers. Notably, the front face of anAPC ferrule is disposed at a nonorthogonal angle, i.e., at other than90°, relative to the longitudinal axis defined by the ferrule. Forexample, the front face of an APC ferrule is commonly disposed at anangle of approximately 8° relative to a plane that extends perpendicularto the longitudinal axis defined by the ferrule. In order tointerconnect a pair of APC ferrules, the ferrules are thereforepositioned such that the angled front faces are complimentary to oneanother, that is, the forwardmost portion of the front face of oneferrule is preferably aligned with the rearwardmost portion of the frontface of the other ferrule and vice versa. In order to facilitate thealignment of the ferrules in this complimentary fashion, the ferrulestypically include a key that is disposed in a predetermined relationshipto the front face of the ferrule. Thus, a connector sleeve or the likecan be utilized to engage the keys of a pair of APC ferrules to insurethat the ferrules are mated in a complementary fashion.

The angled front face of an APC ferrule advantageously reducesundesirable reflections of optical signals at the interface between apair of optical fibers, thereby decreasing optical power losses andcorrespondingly increasing optical power transmission. In addition toforming the ferrule to have a front face that is disposed at apredetermined angle relative to the longitudinal axis defined by theferrule, the front face of some APC ferrules has a spherical shape. Inthis regard, if an APC ferrule is constructed such that the apex of thespherical surface substantially coincides with the bore defined by theferrule, physical contact between the end portions of the respectiveoptical fibers is facilitated, thereby enhancing optical transmissionbetween the optical fibers. Unfortunately, it is relatively difficult toshape the spherical surface of an APC ferrule such that the apex of thespherical surface coincides with the bore defined by the ferrule.Instead, APC ferrules having a spherical front face generally have anapex offset that is defined as the distance by which the apex of thespherical surface is offset from the bore defined by the ferrule. Whilesome apex offset can be tolerated while still maintaining opticaltransmission between the respective optical fibers, signal transmissioncan be adversely impacted if the apex offset becomes too large, such asgreater than 50 microns. The degree of apex offset that can be toleratedis dependent upon several factors including whether the optical fibersare single mode or multimode, as well as the radius of curvature of thespherical surface. In this regard, greater apex offsets are typicallyacceptable for spherical surfaces having larger radii of curvature thanfor spherical surfaces having smaller radii of curvature.

Conventional APC ferrules that are to include a spherical front facetypically require that the amount of material that is removed from thefront face of the ferrule to define the spherical surface be preciselycontrolled so as to form the spherical surface in such a manner that theapex of the spherical surface coincides with the bore defined by theferrule. In this regard, the removal of either too much or too littlematerial during the process of grinding the front face of an APC ferruleinto a spherical shape would typically result in the apex of thespherical surface being offset from the bore defined by the ferrule. Inan attempt to minimize the apex effect, at least some of the priortechniques for grinding the front face of an APC ferrule to define thespherical surface are relatively complex, thereby decreasing theefficiency and increasing the cost at which APC ferrules can befabricated.

One exemplary APC ferrule is described by U.S. Pat. No. 5,351,327 alongwith several techniques for fabricating the APC ferrule. As described,the APC ferrule has a spherically shaped front face with an apex offsetof no more than 50 microns and, more typically, no more than 10 microns.While several different fabrication techniques are described, most ofthe techniques require that the front face of the ferrule be formed intoa temporary surface that is then repolished to form the desiredspherical surface. The temporary surface can be either flat or sphericaland is typically angled or inclined relative to a plane perpendicular tothe longitudinal axis defined by the ferrule. Unfortunately, therepolishing of the front face and the other finishing operationsdisadvantageously consume polishing consumables and reduce theefficiency with which the ferrules can be fabricated.

In addition, U.S. Pat. No. 5,148,660 describes an APC ferrule having aspherical front surface that is angled relative to a plane perpendicularto the longitudinal axis defined by the ferrule. The APC ferruledescribed by U.S. Pat. No. 5,140,660 includes a cylindrical tip orpedestal that extends forwardly from the main portion of the ferrulebody and that has a smaller diameter than the main portion of theferrule body. As such, the cylindrical tip may damage surfaces that comeinto contact with the front face of the ferrule, such as by tearingpolishing film or cleaning clothes.

While a number of APC ferrules have therefore been proposed that includespherical front faces, each of these conventional APC ferrules issubject to some shortcomings. For example, the process of grinding thefront face of the ferrule may have to be closely monitored since theremoval of too much or too little material may disadvantageouslyincrease the apex offset. In addition, some APC ferrules may requireextensive polishing or other finishing operations such that the frontface is sufficiently smooth, thereby increasing the fabrication costsand the resulting cost of the APC ferrules. Thus, with increasingemphasis being placed upon lowering the cost of ferrules and reducingthe permissible tolerances of the ferrules, an improved APC ferrule isdesired that offers a reduced apex offset and that can be fabricated ina relatively simple fashion, thereby reducing fabrication costs and thecost of the resulting APC ferrules relative to conventional fabricationtechniques.

SUMMARY OF THE INVENTION

A ferrule is therefore provided that can be fabricated in a repeatableand an efficient manner so as to have a relatively small apex offset. Inthis regard, a method and apparatus for fabricating a ferrule are alsoprovided that grind a portion of the front face of the ferrule into ahemispherical shape with a relatively small apex offset regardless ofthe amount of material that is removed from the front face of theferrule. Since the apex offset is not dependent upon the amount ofmaterial removed from the front face of the ferrule to define thehemispherical surface, the method and apparatus for fabricating theferrule can be performed in a repeatable manner with a minimum number offinishing steps being required after the grinding process to completethe fabrication of the ferrule.

According to one advantageous aspect of the present invention, a ferruleis provided that includes a ferrule body extending lengthwise betweenopposed front and rear faces and defining a longitudinal axis. Theferrule body also defines a lengthwise extending bore capable ofreceiving an end portion of an optical fiber. According to the presentinvention, the front face of the ferrule body includes a plateaudefining a plane that extends perpendicular to the longitudinal axis anda hemispherical portion through which the bore opens. Typically, thehemispherical portion is rearward of the plateau such that the plateaudefines the forwardmost portion of the ferrule body.

The hemispherical portion of the front face of the ferrule body ispreferably angled relative to the plateau and to the plane perpendicularto the longitudinal axis defined by the plateau. In this regard, a planetangent to the hemispherical portion at a point coincident with thelongitudinal axis is disposed at an offset angle, typically between 8°and 12°, relative to the plane perpendicular to the longitudinal axissuch that the resulting ferrule is an APC ferrule. The plateau isgenerally smaller than the hemispherical portion with the plateautypically extending across less than 50% of the front face of theferrule body, and the hemispherical portion extending across more than50% of the front face of the ferrule body. The plateau is also typicallydisposed proximate a side surface of the ferrule body and, in instancesin which a portion of the ferrule body proximate the front face ischamfered, the plateau is preferably disposed proximate the chamfer.

By constructing the ferrule to have a front face that includes a plateauand a hemispherical portion, the ferrule of the present inventionprovides an angled front face for minimizing reflections and forfacilitating optical coupling with the optical fiber upon which theferrule is mounted. In addition, the ferrule of the present inventioncan be readily fabricated such that the apex offset that is bothrepeatable and relatively small.

According to another aspect of the present invention, a method andapparatus for fabricating a ferrule, such as an APC ferrule, areprovided. In this regard, the ferrule is initially secured within amounting fixture, such as a collet, such that the front face of theferrule is exposed. At this initial stage of the fabrication process,the front face of the ferrule is typically perpendicular to thelongitudinal axis defined by the ferrule. A grinder is also providedthat includes a spindle adapted for rotation about a spindle axis thatis offset by a predetermined angle, such as between 8° and 12°, from aplane perpendicular to the longitudinal axis. The grinder also includesa grinding wheel mounted upon the spindle for rotation therewith aboutthe spindle axis. To impact the spherical surface, the grinding wheelhas an arcuate grinding surface that generally defines a radius ofcurvature of between 5 mm and 12 mm. The grinder is also adapted torotate both the spindle and the grinding wheel about an offset axis thatis orthogonal to the spindle axis and is coplanar with both the spindleaxis and the longitudinal axis defined by the ferrule. Typically, thegrinder rotates the spindle and the grinding wheel at a faster rateabout the spindle axis than about the offset axis.

At least one of the grinding wheel and the ferrule is then advancedtoward the other by means of a translation device such as a translationstage. In particular, the translation device advances at least one ofthe grinder and the mounting fixture toward the other along a motionaxis that extends parallel to the longitudinal axis and that is coplanarwith the spindle axis, the offset axis, and the longitudinal axis.During this advancement, the grinding wheel is rotated about both thespindle axis and the offset axis in order to engage and grind a portionof the front face of the ferrule into a hemispherical shape. Typically,the advancement of at least one of the grinder and the mounting fixtureis halted prior to grinding all of the front face of the ferrule into ahemispherical shape such that a portion of the front face of the ferruleremains as a plateau that extends substantially perpendicular to thelongitudinal axis defined by the ferrule.

While either or both of the grinder and the mounting fixture can beadvanced toward the other, a translation stage typically advances thegrinder toward the ferrule along the motion axis, while the mountingfixture remains fixed in position. In order to insure that the properportion of the front face of the ferrule is ground into a hemisphericalshape, the position of at least one of the ferrule and the grinder isadjusted relative to the other before commencing grinding. In thisregard, the apparatus can include a plurality of adjustment stages foradjusting the position of the mounting fixture in respective planesrelative to the grinder.

By fabricating the ferrule according to the method and apparatus of thepresent invention, a ferrule having an at least partially angled frontface and a relatively small apex offset, such as 50 microns or less, canbe fabricated in a repeatable and an efficient manner. In this regard,since the front face of the ferrule has both a plateau and ahemispherical portion, the apex offset is not dependent upon the amountof material removed from the front face during the process of grindingthe hemispherical surface. As such, ferrules can be repeatedlyfabricated that have approximately the same relatively small apexoffset. In addition, the method and apparatus for fabricating theferrule of the present invention also minimizes finishing steps thatwould otherwise have to be taken in order to complete the fabrication ofthe ferrule, such as by minimizing the subsequent polishing of the frontface of the ferrule since the grinding procedure also produces arelatively hemispherical surface. Thus, the efficiency of thefabrication process is increased and the costs of fabrication arepotentially decreased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of the front face of the ferrule according to oneembodiment of the present invention.

FIG. 2 is a cross-sectional view of the ferrule of FIG. 1 taken alongline 2—2.

FIG. 3 is a schematic representation of the front face of a ferruleaccording to one embodiment of the present invention illustrating theplateau and the hemispherical portion in more detail.

FIG. 4 depicts an apparatus for fabricating a ferrule according to oneembodiment to the present invention.

FIG. 5 is a cross-sectional view of a ferrule and a ferrule holder forholding the ferrule during the grinding process.

FIG. 6 is a schematic representation of at least a portion of anapparatus for fabricating a ferrule according to one embodiment of thepresent invention that illustrates the spindle and the grinding wheel inmore detail.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

An APC ferrule 10, such as an ST, SC, or FC ferrule, is provided thatcan be efficiently and repeatedly fabricated. As shown in FIGS. 1 and 2,the ferrule includes a ferrule body 12 extending lengthwise between theopposed front and rear faces 14, 16. The ferrule is typically formed ofa ceramic material, but can be formed of other materials, such as glass,if so desired. The ferrule body is generally cylindrical and defines alengthwise extending bore 18 for receiving the end portion of an opticalfiber such that the ferrule can be mounted thereupon. In this regard,the portion of the bore proximate the rear face of the ferrule body cantaper radially outward in order to provide a lead-in section 20 forfunneling the optical fiber into the bore. Typically, the APC ferrule isdesigned to be mounted upon a single optical fiber, such as either asingle-mode optical fiber or a multi-mode optical fiber.

The ferrule body 12 also defines a longitudinal axis 22 extendinglengthwise between the opposed front and rear faces 14, 16 along thecenter line of the ferrule body. In addition, the bore is also typicallycentered about the longitudinal axis. The ferrule can also include achamfer 24 proximate the front face to facilitate the insertion andalignment of a ferrule within a connector sleeve or the like and toreduce the size of the front face that must be ground and polished.Typically, the chamfer defines a 30° angle with respect to longitudinalaxis. However, the chamfer can define other angles with respect tolongitudinal axis, if so desired.

According to the present invention, the front face 14 of the ferrulebody 12 is formed to include a plateau 26 and a hemispherical portion28. As depicted in FIGS. 1-3, the plateau defines a plane (designated 30in FIG. 3) that extends perpendicular to the longitudinal axis 22 of theferrule body. In contrast, the hemispherical portion defines a sphericalshape that is angled somewhat relative to the plane that extendsperpendicular to the longitudinal axis, thereby providing an angledfront face that facilitates contact between the front face of theferrule and another APC ferrule. Among other things, this physicalcontact reduces attenuation, typically to less than 0.3 dB with anaverage of about 0.1 dB. As shown, the plateau is preferably theforwardmost portion of the ferrule 10 with the hemispherical portionbeing continuous with the plateau, but generally disposed somewhatrearward of the plateau. In addition, the hemispherical portion isformed such that the bore 18 defined by the ferrule body opens throughthe hemispherical portion. As such, the hemispherical portion typicallyextends across more than 50% of the front face of the ferrule body withthe plateau extending across the remainder, i.e., less than 50%, of thefront face of the ferrule body. In addition, the plateau is typicallydisposed proximate a side surface of the ferrule body and, moreparticularly, proximate the chamfered portion 24 of the side surface ofthe ferrule.

The hemispherical portion 28 of the front face 14 is preferably angledsuch that a plane 32 at a point coincident with the longitudinal axis22, i.e., coincident with the center line of the ferrule 10, is disposedat an angle θ relative to the plane 30, which is perpendicular to thelongitudinal axis and as depicted schematically in FIG. 3. The offsetangle is typically between 8° and 12° and, most typically, is 8°. Assuch, plane 32 is oftentimes called the 8° plane. By having an angledfront face, the ferrule 10 of the present invention reducesdisadvantageous reflections of the optical signals and facilitates thecoupling of the optical signals between a pair of optical fibers uponwhich ferrules of the present invention are mounted. For example, theferrule typically reduces the optical reflections to −70 to −75 dBrelative to the optical signals being transmitted.

As a result of its construction, the ferrule 10 also has a relativelysmall apex offset, that is, a relatively small offset between the apex34 of the hemispherical surface and the bore 18 defined by the ferrule.In this regard, the apex is defined as the point on the hemisphericalsurface that protrudes the furthest outward from the ferrule body 12relative to the plane 32. As noted above, plane 32 is disposed at anangle θ relative to plane 32 and is coincident with the bore. By way ofexample, FIG. 3 depicts a somewhat exaggerated apex offset D between theapex and the bore with the plane 32 depicted for purposes ofexplanation. Typically, the apex offset is less than 50 microns and, insome instances, is less than 10 microns with an average apex offset ofapproximately 30 microns. While an apex offset of 50 microns isgenerally sufficient to provide optical coupling between a pair ofoptical fibers upon which APC ferrules are mounted, APC ferrules thathave a hemispherical portion 28 with a smaller radius of curvature mayrequire an even smaller apex offset, such as 10 microns or less, inorder to provide the desired optical coupling. In this regard, thehemispherical portion typically defines a radius of curvature between 5millimeters and 12 millimeters. For a hemispherical portion having aradius of curvature of 5 millimeters, the ferrule of the presentinvention is particularly advantageous since the apex of thehemispherical surface can be repeatedly positioned to be within arelatively small distance, such as 10 microns or less, of the bore.

The ferrule 10 of the present invention can advantageously be fabricatedin an efficient and repeatable manner by a method and an apparatusprovided according to other aspects of the present invention. In thisregard, the apparatus 40 for fabricating the ferrule includes a mountingfixture 42 for securely holding the ferrule such that the front face 14of the ferrule is exposed. See FIG. 4. Prior to the grinding processdescribed below, the front face of the ferrule is generally planar andis perpendicular to the longitudinal axis 22 defined by the ferrule body12. As shown in FIG. 5, the ferrule is also typically mounted in aferrule holder 44 during the grinding process. As shown, the ferruleholder defines a well 46 that opens through one end for snugly receivingthe rear end of the ferrule. Preferably, the well defined by the ferruleholder is sized such that a predetermined length of the ferrule (termedthe “press length”) extends outwardly beyond the ferrule holder. In oneembodiment, the mounting fixture is a collet 43 in which the ferruleholder and the ferrule are inserted. In particular, the collet of thisembodiment includes a plurality of collet jaws 43 for engaging the sidesurface of the ferrule, as shown in FIG. 4.

The apparatus 40 for fabricating the ferrule 10 also includes a grinder48. As depicted schematically in FIG. 6, the grinder includes a spindle50 adapted for rotation about a spindle axis 52 and a grinding wheel 54mounted upon the spindle for rotation therewith about the spindle axis.Typically, the grinding wheel includes an outer grinding surface 56 thatincludes grit of a predetermined size to facilitate grinding of thefront face of the ferrule. In one embodiment, for example, the grindingsurface may include diamond granules or grit having an average size ofabout 15 microns. In order to form the hemispherical portion 28 of thefront face 14 of the ferrule as described below, the grinding surface ofthe grinding wheel is preferably arcuate and defines a predeterminedradius of curvature. In order to form a hemispherical surface having aradius of curvature between 5 millimeters and 12 millimeters, thearcuate grinding surface of the grinding wheel also preferably defines aradius of between 5 millimeters and 12 millimeters since the radius ofcurvature of the arcuate grinding surface defines the correspondingradius of curvature of the resulting hemispherical portion of the frontface of the ferrule.

The apparatus 40 for fabricating the ferrule 10 also preferably includesa plurality of adjustment stages 58 for adjusting the position of atleast one of the mounting fixture 42 and the grinder 48 in respectiveplanes relative to the other of the mounting fixture and the grinder.Typically, the mounting fixture is positioned in respective planesrelative to the grinder by the plurality of adjustment stages. In thisregard, the plurality of adjustment stages can adjust the position ofthe mounting fixture in at least two orthogonal directions, such as anupward/downward direction and a lateral direction. The position of themounting fixture and, in turn, the ferrule, can be accurately alignedwith respect to the grinding wheel 52.

In addition to rotating the spindle 50 and the grinding wheel 54 aboutthe spindle axis 52, the grinder 48 is also adapted to rotate both thespindle and the grinding wheel about an offset axis 60 as depicted inFIG. 6. As shown, the offset axis is perpendicular to the spindle axisand is coplanar with both the spindle axis and the longitudinal axis 22defined by the ferrule body 12. The grinder is adapted to rotate thespindle and the grinding wheel about the spindle axis at a faster rate,however, than the rate at which the grinder rotates both the spindle andthe grinding wheel about the offset axis. For example, the grindertypically rotates the spindle and the grinding wheel about the spindleaxis at a rate of approximately 10,000 rpm, while the grinder rotatesthe spindle and the grinding wheel about the offset axis at a rate ofabout 60 rpm. As a result of the simultaneous rotation about the spindleaxis and the offset axis and the arcuate shape of the grinding surface,the grinder can impart the desired hemispherical shape to a portion 28of the front face 14 of the ferrule 10.

The apparatus 40 for fabricating the ferrule 10 also includes atranslation device 62, such as a translation stage, for advancing atleast one of the grinder 48 and the mounting fixture 42 toward the otheralong a motion axis 64. While either or both of the grinder and themounting fixture can be moved toward the other along the motion axis,the grinder is typically carried by the translation stage that iscontrollably moved along a linear slide, while the mounting fixturegenerally fixes the ferrule in position following alignment of theferrule with respect to the grinding wheel 54. As such, the translationstage generally advances the grinder toward the ferrule along the motionaxis defined by the linear slide at a predetermined feed rate. As shownschematically in FIG. 6, the motion axis extends parallel to thelongitudinal axis 22 defined by the ferrule body 12 and is coplanar withthe spindle axis 52, the offset axis 60 and the longitudinal axis.

During the advancement of the grinder 48 toward the ferrule 10, thegrinder rotates the spindle 50 and the grinding wheel 54 about both thespindle axis 52 and the offset axis 60, albeit at different rates asdescribed above. Once the grinding surface 56 of the grinding wheelengages the front face 14 of the ferrule, the simultaneous rotation ofthe grinding wheel about both the spindle axis and the offset axisimparts a hemispherical shape to a portion 28 of the front face due tothe arcuate shape of the grinding surface.

Typically, the rates at which the grinder rotates the spindle and thegrinding wheel about the spindle axis and the offset axis as well as thefeed rate at which the translation device 62 advances the grinder towardthe ferrule define the material removal rate, with increased rates ofrotation and/or an increased feed rate correspondingly increasing thematerial removal rate. While the grinder 48 can be advanced at differentfeed rates, the grinder of one embodiment is advanced at a feed rate ofabout 0.06 mm/sec.

As a result of the spindle axis being offset from the plane 30perpendicular to the longitudinal axis 22 defined by the ferrule body 12by the predetermined offset angle θ, typically between 8° and 12°, andthe offset axis being correspondingly offset by the same predeterminedangle from the longitudinal axis defined by the ferrule, thehemispherical surface is angled as described above.

The translation stage continues to advance the grinder 48 toward theferrule 10 until a hemispherical portion 28 of the desired size has beenformed. In this regard, since the ferrule extends beyond the ferruleholder 44 by a predetermined distance, i.e., the press length, and sincethe respective positions of the grinding wheel 54 and the mountingfixture 42 can be precisely determined with a laser micrometer or thelike, the translation stage can controllably advance the grinder apredetermined distance toward the ferrule, with the predetermineddistance being selected such that the hemispherical portion of thedesired size is thereby formed. As shown in FIG. 2, the hemisphericalportion is preferably sized so as to encompass more than half of thefront face 14 of the ferrule and to include that portion of the frontface of the ferrule through which the bore 18 opens. However,advancement of the grinder toward the ferrule is preferably halted whilethe front face of the resulting ferrule still includes a plateau 26 soas to prevent unnecessary wear of the grinding wheel.

As a result of the fabrication technique of the present inventionincluding the simultaneous rotation of the spindle 50 and the grindingwheel 54 about both the spindle axis 52 and the offset axis 60 and theconcurrent advancement of the grinder 48 toward the ferrule 10 along themotion axis 64, the resulting hemispherical portion 28 has an apex 34that is either coincident with or spaced only slightly from the bore 18,regardless of the depth to which the ferrule is ground. Thus, thefabrication method is repeatable such that the resulting ferrules are ofa consistent quality.

According to the present invention, the plateau 26 is designed toaccommodate any differences in the press length of the ferrule 10, thatis, the length of the ferrule that extends beyond the ferrule holder 44.In this regard, if the ferrule is either slightly longer than normal oris not pressed as deeply as normal into the well 46 defined by theferrule holder, the grinder 48 will actually move more materialresulting in a larger hemispherical portion 28 and a smaller plateau. Incontrast, a slightly shorter ferrule or a ferrule that is pressed moredeeply into the well defined by the ferrule holder will be ground lesssuch that the plateau will be larger and the hemispherical portion willbe smaller. In either instance, however, the apex of the hemisphericalportion will still either be coincident with or only slightly offsetfrom the bore 18 defined by the ferrule and the amount of any apexoffset will be consistent irrespective of mount of material that isremoved.

In addition, the fabrication method of the present invention is quiteefficient and the resulting hemispherical surface 28 need only beslightly polished in order to complete the fabrication process. In thisregard, the size of the grit carried by the grinding wheel 54 and therate at which the grinding wheel is rotated about the spindle axis 52generally defines the surface roughness. For a grinding wheel withdiamond grit of 15 microns and rotating at 10,000 rpm, the hemisphericalportion of the front face 14 of the ferrule 10 is generally quite smoothwith a surface roughness of about 100 to 400 nanometers as measured peakto valley. In addition, the plateau generally need not be polished,thereby further conserving polishing consumables and reducingfabrication time. As such, the ferrule does not require extensivepost-grinding operations and the resulting fabrication costs maytherefore be reduced relative to conventional techniques for fabricatingAPC ferrules.

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. Therefore, it is to be understood that theinvention is not to be limited to the specific embodiments disclosed andthat modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

That which is claimed:
 1. A ferrule comprising: a ferrule body extendinglengthwise between opposed front and rear faces to thereby define alongitudinal axis, said ferrule body defining a lengthwise extendingbore capable of receiving an end portion of an optical fiber; whereinsaid front face of said ferrule body includes a plateau defining a planethat extends perpendicular to the longitudinal axis and a hemisphericalportion through which the bore opens.
 2. A ferrule according to claim 1wherein the hemispherical portion is rearward of the plateau.
 3. Aferrule according to claim 1 wherein a plane coincident with the bore isdisposed at an offset angle to the plane perpendicular to thelongitudinal axis.
 4. A ferrule according to claim 3 wherein a planecoincident with the bore is disposed at an offset angle of between about8° and about 12° relative to the plane perpendicular to the longitudinalaxis.
 5. A ferrule according to claim 1 wherein said plateau extendsacross less than 50% and said hemispherical portion extends across morethan 50% of the front face of said ferrule body.
 6. A ferrule accordingto claim 1 wherein said ferrule body includes a side surface extendingbetween the opposed front and rear faces, and wherein said plateau isdisposed proximate the side surface of said ferrule body.
 7. A ferruleaccording to claim 1 wherein a portion of said ferrule body proximatethe front face is chamfered.
 8. A ferrule comprising: a ferrule bodyextending lengthwise between opposed front and rear faces, said ferrulebody having a lengthwise extending bore defining a longitudinal axis,said bore capable of receiving an end portion of an optical fiber,wherein said front face of said ferrule body includes a compound surfacehaving a first surface and a second surface, said first surface having aplateau defining a plane that extends perpendicular to the longitudinalaxis and said second surface having a hemispherical portion throughwhich the bore opens.
 9. The ferrule according to claim 8 wherein thesecond surface is rearward of the first surface.
 10. The ferruleaccording to claim 8 wherein a plane coincident with the bore isdisposed at an offset angle to the plane perpendicular to thelongitudinal axis.
 11. The ferrule according to claim 10 wherein theplane coincident with the bore is disposed at an offset angle of between8° and 12° relative to the plane perpendicular to the longitudinal axis.12. The ferrule according to claim 8 wherein said first surface extendsacross less than 50% and said second surface extends across more than50% of the front face of said ferrule body.
 13. The ferrule according toclaim 8 wherein said ferrule boby includes a side surface extendingbetween the opposed front and rear faces, and wherein said first surfaceis disposed proximate the side surface of said ferrule body.
 14. Theferrule according to claim 8 wherein a portion of said ferrule bodyproximate the front face is chamfered.